1. Field of the Invention
The present invention relates generally to fluid delivery devices for infusion of beneficial agents into a patient. More particularly, the invention concerns a fluid delivery apparatus which includes a conformable ullage and a novel fill assembly for filling the fluid reservoir of the apparatus in the field.
2. Discussion of the Invention
Many medicinal agents require an intravenous route for administration thus bypassing the digestive system and precluding degradation by the catalytic enzymes in the digestive tract and the liver. The use of more potent medications at elevated concentrations has also increased the need for accuracy in controlling the delivery of such drugs. The delivery device, while not an active pharmacologic agent, may enhance the activity of the drug by medicating its therapeutic effectiveness. Certain classes of new pharmacologic agents possess a very narrow range of therapeutic effectiveness, for instance, too small a dose results in no effect, while too great a dose results in toxic reaction.
In the past, prolonged infusion of fluids has generally been accomplished by gravity flow methods, which typically involve the use of intravenous administration sets and the familiar bottle suspended above the patient. such methods are cumbersome, imprecise and require bed confinement of the patient. Periodic monitoring of the apparatus by the nurse or doctor is required to detect malfunctions of the infusion apparatus.
One of the most versatile and unique fluid delivery apparatus developed in recent years is that developed by one of the present inventors and described in U.S. Pat. No. 5,205,820. The components of this novel fluid delivery apparatus generally include: a base assembly, an elastomeric membrane serving as a stored energy means, fluid flow channels for filling and delivery, flow control means, a cover, and an ullage which comprises a part of the base assembly. The ullage in these devices, that is the amount of the fluid reservoir or chamber that is not filled by fluid, is provided in the form of a semi-rigid structure having flow channels leading from the top of the structure through the base to inlet or outlet ports of the device. Since the inventions described herein represent improvements over those described in U.S. Pat. No. 5,205,820 this patent is hereby incorporated by reference as though fully set forth herein.
In the semi-rigid ullage configuration described in U.S. Pat. No. 5,205,820, wherein the ullage means is more fully described, the stored energy means of the device must be superimposed over the ullage to form the fluid-containing portion of the reservoir from which fluids are expelled at a controlled rate by the elastomeric membrane of the stored energy means tending to return to a less distended configuration in the direction toward the ullage. With these constructions, the stored energy membrane is typically used at higher extensions over a significantly large portion of the pressure-deformation curve.
For good performance, the elastomeric membrane materials selected for construction of the stored energy membrane must have good memory characteristics under conditions of high extension; good resistance to chemical and radiological degradation; and appropriate gas permeation characteristics depending upon the end application to be made of the device. Once an elastomeric membrane material is chosen that will optimally meet the desired performance requirements, there still remain certain limitations to the level of refinement of the delivery tolerances that can be achieved using the semi-rigid ullage configuration. These result primarily from the inability of the semi-rigid ullage to conform to the shape of the elastomeric membrane near the end of the delivery period. This nonconformity can lead to extended delivery rate tail-off and higher residual problems when extremely accurate delivery is required. For example, when larger volumes of fluid are to be delivered, the tail-off volume represents a smaller portion of the fluid amount delivered and therefore exhibits much less effect on the total fluid delivery profile, but in very small doses, the tail-off volume becomes a larger portion of the total volume. This sometimes places severe physical limits on the range of delivery profiles that may easily be accommodated using the semi-rigid ullage configuration.
As will be better appreciated from the discussion which follows, the apparatus of the present invention provides a unique, disposable fluid dispenser of simple but highly reliable construction that may be adapted to a wide variety of end use applications. A particularly important aspect of the improved apparatus is the incorporation of conformable ullages made of yieldable materials which uniquely conform to the shape of the stored energy membrane as the membrane distends and then returns to a less distended configuration. This novel construction, which permits the overall height of the device to be minimized, will satisfy even the most stringent delivery tolerance requirements and uniquely overcomes the limitation of materials selection. Further a plurality of subreservoirs can be associated with a single ullage thereby making it possible to incorporate a wide variety of delivery profiles within a single device.
The thrust of the present invention is to provide a novel fluid delivery apparatus that includes a conformable ullage of the character described in the preceding paragraph and also includes a unique fill assembly that can be used to controllably fill the fluid reservoir of the apparatus in the field. As will be better understood from the description which follows, the fill assembly of the present invention includes a fluid containing vial subassembly mounted within a unique adapter subassembly that functions to conveniently mate the vial subassembly with the conformable ullage type fluid delivery assembly.
In use, the adapter subassembly of the invention securely interconnects the fluid containing vial with the fluid delivery assembly so that the reservoir of the device can be controllably filled with the fluid contained within the vial assembly. After the reservoir is thus filled, the stored energy means of the fluid delivery device will cooperate with the conformable ullage to controllably expel the fluid from the device.